The transcription factor AP-1 (activator protein-1) is a DNA binding protein complex composed of gene products of protooncogenes c-jun and c-fos and has been studied as a factor for controlling gene expression which is stimulated by a tumor promoter such as phorbol 12-myristate 13-acetate (PMA) or the like through the binding to its specific DNA sequence. Recently, it has been shown that, in addition to PMA, AP-1 activity is also controlled by various growth factors, cytokine, oncogene which causes transformation and ultraviolet light, and a close relation of AP-1 control to growth, differentiation and malignant alteration of cells has been reported (Biochimica et Biophysica Acta, 1072, 129-157 (1991)).
As an essential gene for maintaining the higher-order structure of a chromosome in Schizosaccharomyces pombe, crm1.sup.+ (chromosome region maintenance) has been reported in 1989 (The Journal of Cell Biology, 108, 1195-1207 (1989)). This crm1.sup.+ is essential for cell growth and a cold sensitive crm1 mutant of the fission yeast shows an abnormal nucleus morphology such as fiber or rod shape at the restrictive temperature. Further, it has such a character that it accumulates a large amount of a new protein of 25 kDa (p25) in the cells. This gene product is a protein composed of 1078 amino acid residues and localized in the nucleus (The Journal of Cell Biology, 108, 1195-1207 (1989)). The more recent study has shown that crm1.sup.+ inhibits the activity of pap1.sup.+ (pombe AP-1), which is a homologous gene of the transcription factor c-Jun/AP-1 of mammalian cells, in the fission yeast (Molecular and Cellular Biology, 12, 5474-5484 (1992)). The above-described p25 is one of genes whose transcriptions are controlled by pap1.sup.+ and the accumulation of p25 protein in a large amount in the above mutant is considered to be caused by functional acceleration of pap1.sup.+ due to functional defect of crm1.sup.+. Furthermore, pap1.sup.+ binding protein, pad1.sup.+, has been newly found in the above yeast and this protein has been shown to have the function of promoting pap1.sup.+ activity (Journal of Cell Science, 108, 569-579 (1995)). Recently, JAB1 gene, human homologous gene of pad1.sup.+, has been isolated and it has been shown that the gene also accelerates the transcription activation capability of a jun family transcription activating factor in human cells by binding to the factor (Nature, 383, 453-457 (1996)).